Archiv für den Monat: April 2014
PostgreSQL: Neues Index-Bloat-Query
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WITH btree_index_atts AS ( SELECT nspname, relname, reltuples, relpages, indrelid, relam, regexp_split_to_table(indkey::text, ' ')::smallint AS attnum, indexrelid as index_oid FROM pg_index JOIN pg_class ON pg_class.oid=pg_index.indexrelid JOIN pg_namespace ON pg_namespace.oid = pg_class.relnamespace JOIN pg_am ON pg_class.relam = pg_am.oid WHERE pg_am.amname = 'btree' ), index_item_sizes AS ( SELECT i.nspname, i.relname, i.reltuples, i.relpages, i.relam, s.starelid, a.attrelid AS table_oid, index_oid, current_setting('block_size')::numeric AS bs, /* MAXALIGN: 4 on 32bits, 8 on 64bits (and mingw32 ?) */ CASE WHEN version() ~ 'mingw32' OR version() ~ '64-bit' THEN 8 ELSE 4 END AS maxalign, 24 AS pagehdr, /* per tuple header: add index_attribute_bm if some cols are null-able */ CASE WHEN max(coalesce(s.stanullfrac,0)) = 0 THEN 2 ELSE 6 END AS index_tuple_hdr, /* data len: we remove null values save space using it fractionnal part from stats */ sum( (1-coalesce(s.stanullfrac, 0)) * coalesce(s.stawidth, 2048) ) AS nulldatawidth FROM pg_attribute AS a JOIN pg_statistic AS s ON s.starelid=a.attrelid AND s.staattnum = a.attnum JOIN btree_index_atts AS i ON i.indrelid = a.attrelid AND a.attnum = i.attnum WHERE a.attnum > 0 GROUP BY 1, 2, 3, 4, 5, 6, 7, 8, 9 ), index_aligned AS ( SELECT maxalign, bs, nspname, relname AS index_name, reltuples, relpages, relam, table_oid, index_oid, ( 2 + maxalign - CASE /* Add padding to the index tuple header to align on MAXALIGN */ WHEN 2%maxalign = 0 THEN maxalign ELSE 2%maxalign END + nulldatawidth + maxalign - CASE /* Add padding to the data to align on MAXALIGN */ WHEN nulldatawidth::integer%maxalign = 0 THEN maxalign ELSE nulldatawidth::integer%maxalign END )::numeric AS nulldatahdrwidth, pagehdr FROM index_item_sizes AS s1 ), otta_calc AS ( SELECT bs, nspname, table_oid, index_oid, index_name, relpages, coalesce( ceil((reltuples*(4+nulldatahdrwidth))/(bs-pagehdr::float)) + CASE WHEN am.amname IN ('hash','btree') THEN 1 ELSE 0 END , 0 -- btree and hash have a metadata reserved block ) AS otta FROM index_aligned AS s2 LEFT JOIN pg_am am ON s2.relam = am.oid ), raw_bloat AS ( SELECT current_database() as dbname, nspname, c.relname AS table_name, index_name, bs*(sub.relpages)::bigint AS totalbytes, CASE WHEN sub.relpages <= otta THEN 0 ELSE bs*(sub.relpages-otta)::bigint END AS wastedbytes, CASE WHEN sub.relpages <= otta THEN 0 ELSE bs*(sub.relpages-otta)::bigint * 100 / (bs*(sub.relpages)::bigint) END AS realbloat, pg_relation_size(sub.table_oid) as table_bytes, stat.idx_scan as index_scans FROM otta_calc AS sub JOIN pg_class AS c ON c.oid=sub.table_oid JOIN pg_stat_user_indexes AS stat ON sub.index_oid = stat.indexrelid ) SELECT dbname as database_name, nspname as schema_name, table_name, index_name, round(realbloat, 1) as bloat_pct, wastedbytes as bloat_bytes, pg_size_pretty(wastedbytes) as bloat_size, totalbytes as index_bytes, pg_size_pretty(totalbytes) as index_size, table_bytes, pg_size_pretty(table_bytes) as table_size, index_scans FROM raw_bloat WHERE ( realbloat > 50 and wastedbytes > 50000000 ) ORDER BY wastedbytes DESC; |
PostgreSQL: stats_temp_directory auf RAMDisk
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Putting stats_temp_directory on a ramdisk – schnelle und billige Perfomance-Optimierung; wieviel das im Einzelfall bringt ist unterschiedlich, speziell VACUUM sollte davon aber durchaus profitieren.